This proposal will examine the mechanisms by which heparan sulfates inhibit vascular smooth muscle cell (SMC) proliferation. Aberrant SMC proliferation is a key event in early atherogenesis and is the major cause of the high failure rate of many vascular surgical procedures, including coronary artery bypass grafts (CABG) and percutaneous transluminal coronary angioplasty (PTCA). CABG and PTCA have become very common procedures in the U.S., with over 300,000 performed each year. Restenosis within 1-3 months occurs rn a large fraction (typically >30%) of these cases, greatly limiting the usefulness of these interventions. A hallmark of the restenosis process is intimal SMC hyperplasia during the first two weeks following angioplasty. Of the several inhibitors of SMC proliferation which have been identified, perhaps the best characterized are the complex glycosaminoglycans of the heparan sulfate (HS) family, which includes heparin. Precise elucidation of the mechanisms of action of HS has been hampered by two major problems: l) the lack of heparin- resistant SMC in which to test putative mechanisms of action and 2) the absence of a highly potent, native HS species which could be structurally analyzed and used in mechanism of action studies. We have recently overcome these problems by isolating a panel of heparin-resistant SMC and by using an endothelial cell-derived HS species. Using these powerful tools, we will: l) precisely define the effect of HS on the signal transduction pathways for mitogenesis, 2) determine the effect of HS on gene expression in SMC, including the effect on the induction of specific protooncogenes and growth effector genes, and 3) determine the structure- function relationships of the endothelial cell-derived, highly antiproliferative HS molecule. The causal relationship of any observed effect of EC-HS to the antiproliferative mechanism will be tested using both heparin-resistant cells and inactive heparan sulfate analogs. It is hoped that a detailed understanding of the mechanisms and molecules which suppress SMC proliferation will provide a therapeutic rationale for controlling SMC hyperplasia following CABG and PTCA and may provide important insights into the pathophysiologic mechanisms underlying atherogenesis.